A major fishery in the Santa Barbara Channel, sea urchins are food from fishes to humans. If their numbers grow unchecked, these important grazers can also cause declines in kelp forest flora.
Islands
Figure App.F.12.5.. A figure showing the density of red and purple sea urchins near four of the Channel Islands.
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Mean density (+/- standard error) of red sea urchin Mesocentrotus franciscanus (top) and purple sea urchin Strongylocentrotus purpuratus (bottom) at 14 sites across four islands in Channel Islands National Marine Sanctuary monitored by the PISCO kelp forest monitoring program from 2003–2016. Recently, density of both species has declined at eastern islands (Anacapa and Santa Cruz) and increased at western islands (Santa Rosa and San Miguel). Sea urchins are counted by SCUBA divers swimming along transect lines. Sea urchin density was averaged across all monitoring sites at each island, including sites located inside and outside of marine reserves and conservation areas, to examine course-scale trends by island. At a finer scale, sea urchin density is responding differently inside and outside of some marine protected areas (MPAs) in CINMS. A discussion of MPA effects in CINMS is available in MPA Effects. Data source: PISCO; Figure: R. Freedman/NOAAIsland vs Mainland
Figure App.F.12.6.. The average amount of red and purple sea urchins at several measuring locations on the Channel Islands and the mainland.